Piston pump

ABSTRACT

The invention relates to a piston pump for a vehicle brake system, in particular a slip-controlled hydraulic vehicle brake system. For damping pressure pulsations, the invention proposes proving a throttle, as a place of narrowed cross section, in an outlet conduit of the piston pump.

PRIOR ART

The invention relates to a piston pump as generically defined by thepreamble to the main claim, which is provided in particular for ahydraulic vehicle brake system.

One such piston pump is known from German Patent Disclosure DE 197 32791 A1. The known piston pump has a pump bore, which is mounted in ahydraulic block that forms a pump housing. A piston is guided axiallydisplaceably in the pump bore. In the known piston pump, a bush isinserted into the pump bore, and the piston is axially displaceablyguided in the bush. It is equally possible to guide the piston axiallydisplaceably in the pump bore in the pump housing directly, leaving outthe bush. By mean of an eccentric element, which is disposed on one faceend of the piston and is drivable to rotate, the piston can be driven toexecute a reciprocating stroke motion in the axial direction in the pumpbore, and this motion in a manner known per se brings about the pumpingof fluid.

As disclosed in German Patent Disclosure DE 42 26 646 A1, for example,such piston pumps are typically followed hydraulically by a damperchamber and a throttle, both of which are disposed in the hydraulicblock that forms the pump housing, outside the pump bore and separatelyfrom the piston pump.

ADVANTAGES OF THE INVENTION

A throttle which is disposed in the pump outlet is integrated with thepiston pump of the invention as defined by the characteristics of claim1. The throttle preferably hydraulically follows an outlet valve of thepiston pump; that is, it is disposed downstream of the outlet valve ofthe piston pump. By way of example, the throttle, in the form of abaffle, nozzle or other cross-sectional constriction, can be disposed inthe pump bore or in an outlet conduit in the pump housing. The throttleserves to damp pressure pulsations of the fluid pumped with the pistonpump, which are caused by the piston pump because of its pulsating modeof pumping. Integrating the throttle with the piston pump has theadvantage of dispensing with a separate throttle that requiresaccommodation externally, for instance in a hydraulic block. Anotheradvantage is that a damper chamber downstream of the piston pump, whichin known hydraulic vehicle brake systems is considered necessary, can bedispensed with.

Advantageous features and refinements of the invention defined by themain claim are the subject of the dependent claims.

In a preferred feature defined by claim 2, the piston pump of theinvention has a bush, which is inserted into the pump bore in the pumphousing, and in which the piston is guided axially displaceably. In thisfeature of the invention, the piston pump furthermore has a closurepart, which closes the pump bore in pressure-tight fashion on one faceend of the bush. An outlet conduit of the piston pump is formed by agroove, which is made in the closure part and/or in the bush and whicheither has or forms a narrowed point in order to form the throttle. Thisfeature of the invention has the advantage of not requiring a separatecomponent for the throttle; it enables favorable production of thethrottle, and it has the advantage that the throttle occupies noadditional space; that is, the throttle is integrated in a space-savingway with the piston pump.

The outlet conduit can be embodied for instance as a radial groove in anend edge of a tubular bush. In FIG. 3, the bush has a bush bottom on aface end toward the closure part. The outlet conduit is formed by agroove which is made in an end face of the bush bottom contacting theclosure part and/or in a face of the closure part contacting the bushbottom, and which is covered by the closure part or the bush bottom,respectively. The groove has a narrowed point which forms the throttle.

A relief conduit according to claim 4 has the advantage that in theevent of partial or complete clogging of the throttle, the closure partis pressure-relieved. If the throttle is clogged, then fluid pumped withthe piston pump and emerging from an outlet hole, surrounded by therelief conduit, in the bush bottom flows into the relief conduit, aslong as it passes between the faces contacting one another of the bushbottom and of the closure part, and from the relief conduit it flowspast the throttle into the pump outlet downstream of the throttle. Theeffect of the relief conduit surrounding the outlet hole in the bushbottom is that fluid under pressure acts upon the closure part solely onthe face enclosed by the relief conduit; that is, if the throttle isclogged, the stress on the closure part is limited to the fraction ofthe surface area, contacting the bush bottom, of the closure part thatis enclosed by the relief conduit. As a result, clogging of the throttleis prevented from leading to leakage of the closure part in the pumpbore or to forcing the closure part out of the pump bore in response toa high pressure on the outlet side of the piston pump resulting from theclogged throttle. This prevents self-destruction of the piston pump.

Producing the bush or the closure part as a formed part (claims 6, 7)has the advantage not only that these parts can be produced economicallyand quickly but also that the groove, forming the outlet conduit, in thebush bottom and/or in the face of the closure part contacting the bushbottom can be made in a single operation together with the production ofthe bush or the closure part as applicable. As a result, producing thethrottle entails no additional effort or cost.

The piston pump of the invention is intended in particular as a pump ina brake system of a vehicle and is used to control the pressure in wheelbrake cylinders. Depending on the type of brake system, theabbreviations ABS (anti-lock brake system), TCS (traction controlsystem), VDC (vehicle dynamics control) and EHB (electrohydraulic brakesystem) are used for such brake systems. In the brake system, the pumpserves for instance to return brake fluid from a wheel brake cylinder ora plurality of wheel brake cylinders to a master cylinder (ABS) and/orto pump brake fluid out of a supply container into a wheel brakecylinder or a plurality of wheel brake cylinders (TCS or VDC or EHB). Ina brake system with wheel slip control (ABS or TCS) and/or a brakesystem serving as a steering aid (VDC) and/or an electrohydraulic brakesystem (EHB), the pump is needed. With wheel slip control (ABS or TCS),locking of the wheels of the vehicle during a braking event involvingstrong pressure on the brake pedal (ABS) and/or spinning of the drivenwheels of the vehicle in the event of strong pressure on the gas pedal(TCS) can for instance be prevented. In a brake system serving as asteering aid (VDC), a brake pressure is built up in one or more wheelbrake cylinders independently of an actuation of the brake pedal or gaspedal, for instance to prevent the vehicle from breaking out of thetrack desired by the driver. The pump can also be used in anelectrohydraulic brake system (EHB), in which the pump pumps the brakefluid into the wheel brake cylinder or cylinders if an electric brakepedal sensor detects an actuation of the brake pedal, or in which thepump is used to fill a reservoir of the brake system.

DRAWING

The invention will be described in further detail below in terms of anexemplary embodiment shown in the drawing. Shown are:

FIG. 1, an axial section through a piston pump of the invention; and

FIG. 2, an end view of a closure part of the piston pump of FIG. 1.

DESCRIPTION OF THE EXEMPLARY EMBODIMENT

The preferred, selected piston pump according to the invention, shown inFIG. 1 and identified overall by reference numeral 10, is inserted intoa stepped pump bore 12 which is mounted in a hydraulic block that formsa pump housing 14. The hydraulic block, of which the drawing shows onlya fragment surrounding the piston pump 10, is a constituent part of aslip-controlled hydraulic vehicle brake system not otherwise-shown.Besides the piston pump 10, further hydraulic components such as magnetvalves or pressure reservoirs are inserted into this block and connectedhydraulically with one another and with the piston pump 10 of theinvention.

The piston pump 10 has a piston 16, whose one end, remote from apositive displacement chamber 18, is guided with a guide ring 20 in thepump housing 14 and sealed off with a sealing ring 22. Another end ofthe piston 16, toward the positive displacement chamber 18, is guidedwith a guide ring 24 in a bush 26 of the piston pump 10 and sealed offwith a sealing ring 28. The bush 26 is inserted with a press fit intothe pump bore 12 of the pump housing 14. The press fit creates sealingbetween the inlet and outlet sides, or in other words the low- andhigh-pressure sides of the piston pump 10.

For the pump inlet, an axial blind bore is made in the piston 16 from aside toward the positive displacement chamber 18, and this side isintersected near its bottom by transverse bores 32. The blind andtransverse bores 30, 32 communicate through windows 34 in acircumferential wall 36 of the bush 26 with an inflow bore 38, which ismade radially to the piston pump 10 in the hydraulic block that formsthe pump housing 14.

On the end of the piston 16 toward the positive displacement chamber, acheck valve is made in the form of an inlet valve 40: The inlet valve 40has a valve ball 42 as a valve closing body, which cooperates with aconical valve seat 44 that is made at an orifice of the blind bore 30 ofthe piston 16. A helical compression spring as a valve closing spring 46presses the valve ball 42 against the valve seat 44. The valve ball 42and valve closing spring 46 are received in a valve cage 48, which ismanufactured as a cup-shaped deep-drawn sheet-metal part, with adiameter approximately equivalent to the diameter of the piston 16, andis provided with flow openings 50. The valve cage 48 has an annular step52, with which it rests on a face end, toward the positive displacementchamber 18, of the piston 16. It has an integral, outward-protrudingradial flange 54, against which a helical compression spring in the formof a piston restoring spring 56 presses and in this way retains thevalve cage 48 on the piston 16. At the same time, the radial flange 54retains the guide ring 24 and the sealing ring 28 axially on the piston16 between itself and a support ring 60 that is braced on an annularshoulder 58 of the piston 16.

The piston restoring spring 56, via the radial flange 54 of the valvecage 58, presses the piston 16 in the axial direction against aneccentric element 62, which can be driven to rotate by an electric motorand which in a manner known per se serves to drive the piston 16 toexecute a reciprocating stroke motion.

On a side adjoining the positive displacement chamber 18, the bush 26has an integral bush bottom 64, in the middle of which a continuousoutlet hole 66 of the piston pump 10 is made.

On the side toward the positive displacement chamber, immediatelyadjacent the bush bottom 64 on the face end, a closure part 68 which hasthe form of a cylindrical plug is inserted into the pump bore 12; it issecured and sealed off in fluid-tight fashion by a calking 70 of thepump housing 14 in the pump bore 12. At the same time, the closureelement 68 keeps the bush 26 in the pump bore 12.

On a face end toward the bush 26, a shallow, preferably cylindricalrecess 72 is made in the closure part 68, and the bush 26 is inserted byits end that has the bush bottom 64 into this recess. For fastening theclosure part 68 to the bush 26, the bush 26, on its end inserted intothe closure part 68, has an outward-protruding radial collar 74, whichforms an undercut 76 that is engaged from behind by one edge 78 of therecess 72 in the closure part 68. To cause the edge 78 to engage theundercut 76 from behind, this edge is reshaped radially inward, forinstance by crimping. Crimping the circumference at from three to fourpoints suffices for this fastening.

An axial blind bore 80 is made in the closure part 68, on a bottom ofthe recess 72, and in it a check valve in the form of an outlet valve 82is accommodated; the outlet valve cooperates with a spherical valve seat84, which is made at an orifice, toward the closure part 68, of theoutlet hole 66 in the bush bottom 64. A valve ball 86 as a valve closingbody is inserted into the blind bore 80 of the closure part 68 and isurged against the valve seat 84 by a helical compression spring 88acting as a valve closing spring.

An outer end face 90 of the bush bottom 64 is flat. With this face, thebush bottom 64 rests on a likewise flat bottom face 92 of the recess 72in the closure part 68. A radial groove is made in the bottom face 92and is covered by the bush bottom 64 to form a conduit which forms anoutlet conduit 94 of the piston pump 10. The outlet conduit 94 leadsfrom the blind bore 80 of the closure part 68, in which the outlet valve82 is accommodated, to the outer circumference of the closure part 68;the outlet conduit 94 passes through the edge 78 surrounding the recess72 of the closure part 68 and opens into an annular conduit 96, whichextends around the bush bottom 64 and is surrounded by the pump housing14, the bush bottom 64, and the closure part 68. An outlet bore 98 ismade in the pump housing 14, originating at the annular conduit 96.

FIG. 2 shows an end view on the bottom face 92 of the recess 72 in theclosure part 68. As can readily be seen from FIG. 2, the outlet conduit94 in the bottom face 92 of the recess 72 in the closure part 68narrows; it has a place of narrowed cross section, which forms athrottle 100 integrated with the piston pump 10.

In addition to the radially extending outlet conduit 94, a furthergroove is made in the bottom face 92 of the recess 72 in the closurepart 68; it forms a relief conduit 102. The relief conduit 102 has anapproximately egg-shaped course; it surrounds the blind bore 80 in theclosure part 68, in which the outlet valve 82 is accommodated, as wellas the outlet hole 66 in the bush bottom 64. On its “pointed” end, therelief conduit 102 opens at both ends radially outside the throttle 100,or in other words discharges downstream of the throttle 100 into theoutlet conduit 94. If brake fluid pumped by the piston pump 10 underpressure penetrates between the bottom face 92 of the recess 72 in theclosure part 68 and the bush bottom 64 contacting the bottom face 92 inthe event of clogging of the throttle 100, then at maximum, a surfacearea enclosed by the relief conduit 102 is acted upon by the brake fluidunder pressure. As soon as the brake fluid reaches the relief conduit102 at one point, it flows through it, past the throttle 100 into theoutlet conduit 94 and from there on through the annular conduit 96 intothe outlet bore 98. The relief conduit 102 prevents brake fluid underpressure from acting on the closure part 68 over its entire surface areain the event of clogging of the throttle 100. As a result, failure ofthe calking 70, which retains the closure part 68 in pressure-tightfashion in the pump bore 12, is also averted. The relief conduit 102prevents leakage of the closure part 68 in the pump bore 12 or preventsthe closure part 68 from being forced out of the pump bore 12 if thethrottle 100 is clogged.

The bush 26 is produced in the form of a cold-headed part made of steel;in a single operation with the production of the bush 26, the outlethole 66 and the valve seat 84 are also made in the bush bottom 64. Atmost, postmachining of the valve seat 84 is all that is required. Inthis way, the bush 26 can be produced inexpensively and quickly withoutmetal-cutting machining.

The closure part 68 is made as a cold-headed part of aluminum; theradial groove that forms the outlet conduit 94 together with thethrottle 100 and the relief conduit 102 are made in a single operationtogether with the closure part 68 by cold-heading. Once again this hasmajor cost advantages and saves time in production.

What is claimed is:
 1. In a piston pump, having a pump housing that hasa pump bore (12) and having a piston (16) that is axially displaceablein the pump bore and can be driven to execute an axially reciprocatingstroke motion, the improvement wherein the piston pump (10) has anintegrated throttle (100), which is disposed in a pump outlet (94),wherein the piston pump (10) has a bush (26), which is inserted into thepump bore (12) in the pump housing (14), and in which the piston (16) isguided axially displaceably; wherein the piston pump (10) has a closurepart (68), which is inserted, closing the pump bore (12) inpressure-tight fashion, into the pump bore (12) on one face end of thebush (26); wherein the piston pump (10) has an outlet conduit (94)between the closure part (68) and the bush (26), which conduit is formedby a groove in the closure part (68) and/or in the bush (26); andwherein the outlet conduit (94) has a narrowed point that forms thethrottle (100) of the piston pump (10).
 2. The piston pump of claim 1,wherein the bush (26) has a bush bottom (64) on a face end toward theclosure part; and wherein the groove forming the outlet conduit (94) ismade in a face (92) of the closure part (68) contacting the bush bottom(64) or in a face (90) of the bush bottom (64) contacting the closurepart (68).
 3. The piston pump of claim 2, wherein the bush bottom (64)is pierced by an outlet hole (66) of the piston pump (10); and whereinthe piston pump (10) has a relief conduit (102), which is disposedbetween the bush bottom (64) and the closure part (68) and is formed bya groove, which is made, surrounding the outlet hole (66) in the bushbottom (64), in the bush bottom (64) or in the closure part (68) andwhich communicates with a pump outlet (94) in the flow directiondownstream of the throttle (100).
 4. The piston pump of claim 3, whereinthe piston pump (10) has a check valve as an outlet valve (82), which isdisposed inside the relief conduit (102) in the closure part (68), andan orifice of the outlet hole (66), toward the closure part (68), isembodied in the bush bottom (64) as a valve seat (84) of the outletvalve (82).
 5. The piston pump of claim 1, wherein the bush (26) has abush bottom (64) on a face end toward the closure part; and wherein thegroove forming the outlet conduit (94) is made in a face (92) of theclosure part (68) contacting the bush bottom (64) and in a face (90) ofthe bush bottom (64) contacting the closure part (68).
 6. The pistonpump of claim 5, wherein the bush bottom (64) is pierced by an outlethole (66) of the piston pump (10); and wherein the piston pump (10) hasa relief conduit (102), which is disposed between the bush bottom (64)and the closure part (68) and is formed by a groove, which is made,surrounding the outlet hole (66) in the bush bottom (64), in either thebush bottom (64) or the closure part (68) and which communicates with apump outlet (94) in the flow direction downstream of the throttle (100).7. The piston pump of claim 6, wherein the piston pump (10) has a checkvalve as an outlet valve (82), which is disposed inside the reliefconduit (102) in the closure part (68), and an orifice of the outlethole (66), toward the closure part (68), is embodied in the bush bottom(64) as a valve seat (84) of the outlet valve (82).
 8. The piston pumpof claim 5, wherein the bush bottom (64) is pierced by an outlet hole(66) of the piston pump (10); and wherein the piston pump (10) has arelief conduit (102), which is disposed between the bush bottom (64) andthe closure part (68) and is formed by a groove, which is made,surrounding the outlet hole (66) in the bush bottom (64), in the bushbottom (64) and in the closure part (68) and which communicates with apump outlet (94) in the flow direction downstream of the throttle (100).9. The piston pump of claim 1, wherein the bush (26) is formed as acold-headed part.
 10. The piston pump of claim 1, wherein the closurepart (68) is formed as a cold-headed part.